In the morning, everyone turned into a beast (5)
I believe the answer is:
llama
'a beast' is the definition.
(I know that llama is a type of animal)
'in the morning everyone turned' is the wordplay.
'in the morning' becomes 'am' (AM on a clock).
'everyone' becomes 'all' (all people).
'turned' shows that the letters should be reversed in order.
'am'+'all'='amall'
'amall' in reverse letter order is 'LLAMA'.
'into' is the link.
(Other definitions for llama that I've seen before include "South American animal of the camel family" , "one that ruminates" , "South American cud-chewing mammal" , "mammal that chews cud" , "South American transport animal" .)